Transmissions featuring floating transmission mainshaft gears such as associated with twin countershaft transmissions are well known and examples of which can be found in U.S. Pat. Nos. 3,237,472; 3,238,613; 3,425,290; and 3,885,446, the disclosures of which are incorporated herein by reference.
Such transmissions generally feature a plurality of floating mainshaft gears that encircle the mainshaft and are supported and driven by countershaft gears, typically two countershaft gears, that are mounted on a pair of countershafts disposed spaced-apart parallel relationship on opposite sides of the mainshaft.
The mainshaft gears are characteristically clutched to the mainshaft by means of a clutch mechanism that slides along external splines extending axially along the mainshaft and has radially outwardly extending teeth or splines that meshingly engage internal teeth or splines on the mainshaft gear so as to cause rotation of the mainshaft when the mainshaft gear is clutched thereto.
A problem, long ago recognized, has been the potential for transfer of axial thrust to a floating mainshaft gear closely adjacent to the floating mainshaft gear being clutched to a mainshaft by an axially moving clutch assembly. In view of such, a variety of solutions have been devised over past years for transmitting axial thrust to the mainshaft that has been imparted to a mainshaft gear by an axially moving clutch mechanism rather than the mainshaft gear adjacent the gear being clutched to the mainshaft.
Such solutions have generally been in the form of gear retainer(s) of one type or another that characteristically limit axial movement of the mainshaft gears to prevent them from engaging each other whether or not one of them is being clutched to the mainshaft.
One example of a retainer assembly for limiting axial movement of a transmission gear is disclosed in U.S. Pat. No. 2,397,905, the disclosure of which is incorporated herein by reference. Here however, a costly and expensive pivotable woodruff key is required to lock a thrust collar onto external splines of the mainshaft to prevent a gear from moving axially.
An example of a splined thrust washer for transmitting axial thrust from a gear set to a propeller drive shaft is disclosed in U.S. Pat. No. 3,984,621, the disclosure of which is incorporated herein by reference. Here, a splined thrust washer (52) is slid along the shaft splines to a transverse groove adjacent a stepped shoulder on the shaft and is held in place against the shoulder by a splined collar (30). Thrust washer (52) is operative to transmit axial thrust of only one gear to the propeller shaft and in addition to requiring the use of a collar (30), also requires costly and complex machining of a stepped configuration to the Propeller shaft exterior.
A more recent example of a transmission mainshaft gear retainer for preventing axial movement of two closely spaced gears to prevent transfer of axial thrust force therebetween is disclosed in U.S. Pat. No. 4,034,620, the disclosure of which is incorporated herein by reference. Here, a thrust ring (104) is splined to the mainshaft between two adjacent gears and is held in place by means of snap rings (108, 110) on opposite sides thereof. The gears are further required to have costly and complex mating tongue and groove configurations that operate in conjunction with additional snap ring (102) to limit movement of the gears away from each other.
An even more recent example of a three thrust washer combination for transmitting axial thrust imparted to a mainshaft gear to the mainshaft and upon which the present improvement is founded is disclosed in U.S. Pat. No. 4,949,589, assigned to the assignee of the present invention and the disclosure of which is incorporated herein by reference. Here however, all three washers require relatively large width transverse grooves for their axial containment in the outer surface of the mainshaft that are substantially the same.
The present invention addresses a problem concerning interchangability between the retainer rings and the thrust washer to insure that neither of the retainer rings is inadvertently placed in the thrust ring groove and that the thrust washer is not inadvertently placed in either the retainer ring grooves.
The present invention also overcomes such shortcomings by insuring the adjacent transmission mainshaft gears do not contact each other while one is being clutched to the mainshaft in addition to making the pair of retainer rings interchangeable with each other as well as rendering it impossible to place a retainer ring in the thrust washer groove and to place the thrust washer in either of the retainer ring grooves.